A serving is the amount of food recommended in consumer education materials such as MyPlate. A portion is the amount of a food you choose to eat at any one time â which may be more or less than a serving. Here are some everyday comparisons to help you figure out your serving sizes. 1  1 teaspoon of margarine is the size of one dice. 2  3 ounces of meat is the size of a deck of cards. 3  1 cup of pasta is the size of a baseball. 4  1Â½ ounces of cheese is the size of four stacked dice.
1 If the oxygen concentration in the blood decreases, they tell the respiratory centers to increase the rate and depth of breathing.  Carbon dioxide: Peripheral chemoreceptors also monitor the carbon dioxide concentration in the blood.
The central chemoreceptors do not directly detect the arterial CO 2 tension. Instead, they detect decreases in the CSF pH. These two values are connected because arterial CO 2 diffuses past the blood brain barrier, into the CSF, and is converted by carbonic anhydrase to carbonic acid that in turn decreases the CSF pH.